I have materialzed view which is a member of a refresh group. When i run the following command:

call dbms_refresh.refresh('km_pt.blob_refresh_group')

I am told the call was completed successfully. However the data in the view has not changed in anyway, if i run the SELECT statement that the view is based on independently the changes on the master table are reflected in the retrieved data.

Is there any reason why this would be happening? My code for creating the view is:

Ian,
If you don't have it already do the following:
Shuttdown the databse:
Perform the following tasks into the database
Add the following line to the ini<ora_sid>.ora file

JOB_QUEUE_PROCESSES=1
JOB_QUEUE_INTERVAL=10

and then restart the database

note:
JOB_QUEUE_PROCESSES is the number of the processes running in background.
JOB_QUEUE_INTERVAL is the frequency that the process is waked up to check the snapshots, and to refresh in case of need.(it's not the refresh frequency for the snapshot!)
I hope it will helps,